It sounds like maybe there is a problem with the cable between your DIN modules, or maybe a short on one of the PCBs
Which application is this? What happens with the buttons 3-16, are they all OK like 1 and 2? Are you using momentary switches (switches off when you release it)? Where did you get your PCBs from?
You may like to try some of the testing apps on the download page.
I noticed you have also posted on the French forum: problème DIN So maybe you will get better help in your native tongue